High-efficiency bioenergy production from acorn waste through a sustainable biorefining

Sustainable and non-food-competing bioresources are essential for meeting global energy demands while ensuring food security. Acorn waste represents a promising feedstock for biofuel production within a biorefinery framework. This study investigates three scenarios for biofuel production from acorn wastes, involving acid-catalyzed organosolv pretreatment, solvent extraction (using ethanol, hexane, and water), enzymatic hydrolysis, fermentation with Mucor indicus, anaerobic digestion, and transesterification. In Scenario I, the fermentation of acorn produced 354.9 L of ethanol per ton of waste, equivalent to 235.1 L of gasoline, with 95 % of the energy derived from the kernel. Scenario II focused on anaerobic digestion, yielding 456 m3 of biomethane per ton of acorn waste (dry mass), equal to 514.5 L of gasoline equivalent, with 40.8 % of energy from the extracted kernel. Scenario III integrated ethanol and biogas production with lignin recovery, resulting in 354.6 L of ethanol, 209.2 m3 of biomethane, and 642 kg of lignin per ton, totaling 557.6 L of gasoline equivalent. Additionally, acorn kernel oil offered a biodiesel feedstock equivalent to 47.4 L of gasoline per ton. Overall, the integrated biorefinery approach significantly enhanced energy and material recovery from acorn waste, presenting a highly efficient and sustainable route for advanced biofuel production.